(2) 4x²-3x=0,x(4x-3)=0,
x=0或 4x-3=0, ∴ x1=-1, x2=3/4.
(3)3(x+1)=x(x+1),(x+1)(3-x)=0,
x+1=0或3-x=0∴x1=-1,x2=3.
(4)x²-6x-7=0, (x+l) (x-7)=0,
x+1=0或 x-7=0, ∴x1=-1 ,x2=7.
(5)t(t+3)=28, t²+3t-28=0,
(t+7) (t-4)=0,t+7=0或t-4=0,
∴t1=-7,t2 =4.
(6) (x+l) (x+3) =15, x²+4x-12 =0,
(x+6)(x-2)=0,x+6=0或x-2=0,
∴x1=-6,x2=2.